Source or drain structures with high germanium concentration capping layer

ABSTRACT

Integrated circuit structures having source or drain structures with a high germanium concentration capping layer are described. In an example, an integrated circuit structure includes source or drain structures including an epitaxial structure embedded in a fin at a side of a gate stack. The epitaxial structure has a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer. The lower semiconductor layer includes silicon, germanium and boron, the germanium having an atomic concentration of less than 40% at the abrupt interface. The capping semiconductor layer includes silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% at the abrupt interface and throughout the capping semiconductor layer.

TECHNICAL FIELD

Embodiments of the disclosure are in the field of advanced integrated circuit structure fabrication and, in particular, integrated circuit structures having source or drain structures with a high germanium concentration capping layer.

BACKGROUND

For the past several decades, the scaling of features in integrated circuits has been a driving force behind an ever-growing semiconductor industry. Scaling to smaller and smaller features enables increased densities of functional units on the limited real estate of semiconductor chips. For example, shrinking transistor size allows for the incorporation of an increased number of memory or logic devices on a chip, lending to the fabrication of products with increased capacity. The drive for ever-more capacity, however, is not without issue. The necessity to optimize the performance of each device becomes increasingly significant.

Variability in conventional and currently known fabrication processes may limit the possibility to further extend them into the 10 nanometer node or sub-10 nanometer node range. Consequently, fabrication of the functional components needed for future technology nodes may require the introduction of new methodologies or the integration of new technologies in current fabrication processes or in place of current fabrication processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1G illustrate cross-sectional views representing various operations in a method of fabricating an integrated circuit structure having source or drain structures with a high germanium concentration capping layer, in accordance with an embodiment of the present disclosure.

FIGS. 2A-2F illustrate cross-sectional views representing various operations in a method of fabricating an integrated circuit structure having source or drain structures with a high germanium concentration capping layer, in accordance with an embodiment of the present disclosure.

FIG. 3A illustrates a plan view of a plurality of gate lines over a pair of semiconductor fins, in accordance with another embodiment of the present disclosure.

FIG. 3B illustrates a cross-sectional view, taken along the a-a′ axis of FIG. 3A, in accordance with an embodiment of the present disclosure.

FIG. 4 illustrates a cross-sectional view of an integrated circuit structure having trench contacts for a PMOS device, in accordance with another embodiment of the present disclosure.

FIG. 5 illustrates a cross-sectional view of an integrated circuit structure having a conductive contact on a raised source or drain region, in accordance with an embodiment of the present disclosure.

FIGS. 6A and 6B illustrate cross-sectional views of various integrated circuit structures, each having trench contacts including an overlying insulating cap layer and having gate stacks including an overlying insulating cap layer, in accordance with an embodiment of the present disclosure.

FIG. 7 illustrates a computing device in accordance with one implementation of the disclosure.

FIG. 8 illustrates an interposer that includes one or more embodiments of the disclosure.

FIG. 9 is an isometric view of a mobile computing platform employing an IC fabricated according to one or more processes described herein or including one or more features described herein, in accordance with an embodiment of the present disclosure.

FIG. 10 illustrates a cross-sectional view of a flip-chip mounted die, in accordance with an embodiment of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

Integrated circuit structures having source or drain structures with a high germanium concentration capping layer, and methods of fabricating source or drain structures with a high germanium concentration capping layer, are described. In the following description, numerous specific details are set forth, such as specific integration and material regimes, in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to one skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other instances, well-known features, such as integrated circuit design layouts, are not described in detail in order to not unnecessarily obscure embodiments of the present disclosure. Furthermore, it is to be appreciated that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.

The following detailed description is merely illustrative in nature and is not intended to limit the embodiments of the subject matter or the application and uses of such embodiments. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Any implementation described herein as exemplary is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description.

This specification includes references to “one embodiment” or “an embodiment.” The appearances of the phrases “in one embodiment” or “in an embodiment” do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure.

Terminology. The following paragraphs provide definitions or context for terms found in this disclosure (including the appended claims):

“Comprising.” This term is open-ended. As used in the appended claims, this term does not foreclose additional structure or operations.

“Configured To.” Various units or components may be described or claimed as “configured to” perform a task or tasks. In such contexts, “configured to” is used to connote structure by indicating that the units or components include structure that performs those task or tasks during operation. As such, the unit or component can be said to be configured to perform the task even when the specified unit or component is not currently operational (e.g., is not on or active). Reciting that a unit or circuit or component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. § 112, sixth paragraph, for that unit or component.

“First,” “Second,” etc. As used herein, these terms are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.).

“Coupled.” The following description refers to elements or nodes or features being “coupled” together. As used herein, unless expressly stated otherwise, “coupled” means that one element or node or feature is directly or indirectly joined to (or directly or indirectly communicates with) another element or node or feature, and not necessarily mechanically.

In addition, certain terminology may also be used in the following description for the purpose of reference only, and thus are not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “side”, “outboard”, and “inboard” describe the orientation or location or both of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import.

“Inhibit.” As used herein, inhibit is used to describe a reducing or minimizing effect. When a component or feature is described as inhibiting an action, motion, or condition it may completely prevent the result or outcome or future state completely. Additionally, “inhibit” can also refer to a reduction or lessening of the outcome, performance, or effect which might otherwise occur. Accordingly, when a component, element, or feature is referred to as inhibiting a result or state, it need not completely prevent or eliminate the result or state.

Embodiments described herein may be directed to front-end-of-line (FEOL) semiconductor processing and structures. FEOL is the first portion of integrated circuit (IC) fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) are patterned in the semiconductor substrate or layer. FEOL generally covers everything up to (but not including) the deposition of metal interconnect layers. Following the last FEOL operation, the result is typically a wafer with isolated transistors (e.g., without any wires).

Embodiments described herein may be directed to back end of line (BEOL) semiconductor processing and structures. BEOL is the second portion of IC fabrication where the individual devices (e.g., transistors, capacitors, resistors, etc.) get interconnected with wiring on the wafer, e.g., the metallization layer or layers. BEOL includes contacts, insulating layers (dielectrics), metal levels, and bonding sites for chip-to-package connections. In the BEOL part of the fabrication stage contacts (pads), interconnect wires, vias and dielectric structures are formed. For modern IC processes, more than 10 metal layers may be added in the BEOL.

Embodiments described below may be applicable to FEOL processing and structures, BEOL processing and structures, or both FEOL and BEOL processing and structures. In particular, although an exemplary processing scheme may be illustrated using a FEOL processing scenario, such approaches may also be applicable to BEOL processing. Likewise, although an exemplary processing scheme may be illustrated using a BEOL processing scenario, such approaches may also be applicable to FEOL processing.

In accordance with one or more embodiments of the present disclosure, PMOS source and drain (S/D) melt and re-crystallization for high Ge defect free source and drain and PMOS channel strain is described.

To provide context, high Ge containing SiGe:B PMOS source or drain structures are needed for low contact resistivity. However, the high Ge containing layers are likely to contain crystallographic dislocations resulting in low compressive or even tensile channel strain degrading the channel mobility and drive. Previous solutions have involved either maintaining the Ge concentration low enough to prevent defects or utilizing high Ge but degrading the channel strain. As such, previous solutions have required a compromise between minimizing the resistivity and achieving the maximum channel strain.

In accordance with one or more embodiments described herein, epitaxial deposition of a Ge:B layer capped with a thin extremely low Ge concentration (e.g., less than 5%) and high boron SiGe:B layer on top of a SiGe:B layer with moderate Ge concentrations is described. The resulting structure is exposed to a high temperature anneal that can cause the Ge:B layer to melt. The melted Ge:B layer can then consume the top low Ge concentration layer and, as the Si concentration of the melt increases, the required temperature to maintain a melt increases. Eventually, the Si concentration of the melt can be too high to maintain a melt for the given anneal temperature resulting in the melt recrystallizing. As the melt recrystallizes, the bottom SiGe:B layer can be used as a seed, resulting in a high Ge containing defect free SiGe:B capping layer. The resulting SiGe:B capping layer can have high Ge and high B that will reduce the contact resistivity. Additionally, the capping layer can be defect free and cause an increase in PMOS channel strain.

In accordance with one or more embodiments, the utilization of a precursor cap can be identified via TEM, SIMS, and Atom Probe Tomography (APT). TEMs can show defect free source drains and nanodiffraction analysis of the channel can show high channel strain. SIMS and APT can show that the top of the source drain has a high Ge concentration, e.g., 50% or more, and a high boron concentration. The composition can be determined by the thickness and concentration of each of the starting layers as well as the anneal conditions. Additionally, the bottom portion of high Ge SiGe:B cap can show a gradient in concentration from mixing of the Ge:B layer and the bottom SiGe:B layer.

Implementation of embodiments described herein may include the use of a Ge:B layer deposited in a PMOS source drain and capped with a low Ge SiGe:B film. The Ge:B layer has a melting temperature less than 1000° C. As such, during the anneal, the Ge:B layer melts and the SiGe:B layer diffuses into the Ge:B layer. As either the temperature of the anneal cools down or the Si concentration in the melt increases to a point sufficiently high, the melt starts to re-crystallize. The melt uses the underlying SiGe:B layers in the PMOS source drain as a seeding surface resulting in defect free re-crystallization. It is to be appreciated that the final composition of the SiGe:B layer can be dependent upon the starting composition of the Ge:B layer and the capping SiGe:B layer. For example, if the SiGe:B layer has more Ge, the melt will be starved of Si resulting in the final crystallized layer being higher in Ge. The relative thickness of each layer can vary the process (e.g., if the SiGe:B layer is thin or the Ge:B layer is thick the melt can be starved of Si, resulting in a higher Ge concentration in the final film). In an embodiment, a lower anneal temperatures can lead to a melt that can sustain less Si before re-crystallizing, resulting in a higher Ge concentration in the final film.

In accordance with one or more embodiments described herein, it can be essential for low contact resistance that a metal silicide is in contact with a high-Ge-content layer. As an exemplary process flow, FIGS. 1A-1G illustrate cross-sectional views representing various operations in a method of fabricating an integrated circuit structure having source or drain structures with a high germanium concentration capping layer, in accordance with an embodiment of the present disclosure.

Referring to FIG. 1A, two angled cross-sectional views of a starting structure 100 depict a plurality of semiconductor fins 104 on a substrate 102. In one embodiment, a plurality of silicon fins 104 is continuous with a silicon substrate 102. A patterning mask 106 remains on the plurality of semiconductor fins 104 following formation. In one embodiment, the patterning mask 106 includes a silicon nitride hardmask layer 106A, a carbon hardmask (CHM) layer 106B, a silicon anti-reflective coating layer 106C, and a photoresist layer 106D.

Referring to FIG. 1B, two angled cross-sectional views depict isolation structures 108 between some of the plurality of semiconductor fins 104. Dummy gate lines 110 (such as polysilicon gate lines) are formed over the plurality of semiconductor fins 104. Each of the plurality of semiconductor fins 104 is defined to include sub-fin portions 104A and active fin portions 104B. Isolation liners 109A and isolation caps 109B can be included, as is depicted. A dummy gate hardmask 111 can be included on the dummy gate lines 110, as is also depicted.

Referring to FIG. 1C, a fin cut through source or drain (S/D) cross-sectional view and a PMOS S/D cut through fin cross-sectional view depict PMOS etch-out regions 112 (e.g., trenches), where PMOS source or drain structures will ultimately be formed. Also, depicted are NMOS source or drain structures 114 having an NMOS hardmask layer 116 thereon.

Referring to FIG. 1D, a fin cut through source or drain (S/D) cross-sectional view and a PMOS S/D cut through fin cross-sectional view depict epitaxial growth of a PMOS source or drain precursor structure including a lower relatively low Ge-content source or drain region 118 and an upper germanium layer 120. An extremely low Ge source or drain cap 122 is epitaxially grown on the upper germanium layer 120. In an embodiment, the low Ge-content source or drain region 118 includes silicon, germanium and boron, the germanium having an atomic concentration of less than 40%, the upper germanium layer 120 consists essentially of germanium and boron, and the extremely low Ge source or drain cap 122 includes silicon and boron with little to no germanium. In another aspect, it is to be appreciated that if the final film is sought to be higher in Ge % one method is to increase the Ge % here above the 5%, say to 10 or 20%.

Referring to FIG. 1E, the PMOS source or drain precursor structure of FIG. 1D is subjected to an anneal process. The anneal process melts the upper germanium layer 120 and the extremely low Ge source or drain cap 122, which then mix and recrystallize to form a PMOS source or drain structure including a recrystallized high germanium-content boron-doped silicon germanium capping layer 123. In one embodiment, the melting and recrystallization process results in the formation of an abrupt interface between the low Ge-content source or drain region 118 and the recrystallized high germanium-content boron-doped silicon germanium capping layer 123, e.g., a sharp definition between the two layers as opposed to a blurred or graded or mixed region between the two layers.

Referring to FIG. 1F, a fin cut through source or drain (S/D) cross-sectional view and a PMOS S/D cut through fin cross-sectional view depict replacement of the dummy gate lines 110 with metal gate electrodes (and, possibly corresponding high-k gate dielectrics) of a gate stack 124. Also depicted are partially eroded NMOS source or drain structures 126. The partially eroded NMOS source or drain structures 126 can be formed upon removal of the NMOS hardmask layer 116 from the NMOS source or drain structures 114. In opening the PMOS source or drain structures, the recrystallized high germanium-content boron-doped silicon germanium capping layer 123 may also be slightly etched to form an eroded recrystallized high germanium-content boron-doped silicon germanium capping layer 123′.

Referring to FIG. 1G, a fin cut through source or drain (S/D) cross-sectional view and a PMOS S/D cut through fin cross-sectional view depict formation of a conductive structure on the recrystallized high germanium-content boron-doped silicon germanium capping layer 123 or 123′ of the PMOS source or drain structures. The conductive structure includes a metal silicide layer 128A and a conductive contact 128B/128C which can include a conductive liner 128B and a conductive fill 128C.

With reference again to FIGS. 1A-1G, in accordance with an embodiment of the present disclosure, an integrated circuit structure includes a fin 104 having a lower fin portion 104A and an upper fin portion 104B. A gate stack 124 is over the upper fin portion 104B of the fin 104, the gate stack 124 having a first side opposite a second side. A first source or drain structure (first PMOS S/D) has an epitaxial structure embedded in the fin 104 at the first side of the gate stack 124, the epitaxial structure including a lower semiconductor layer 118 and a capping semiconductor layer 123 or 123′ on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer 123 or 123′ and the lower semiconductor layer 118. A second source or drain structure (second PMOS S/D) has an epitaxial structure embedded in the fin 104 at the second side of the gate stack 124, the epitaxial structure including a lower semiconductor layer 118 and a capping semiconductor layer 123 or 123′ on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer 123 or 123′ and the lower semiconductor layer 118. The lower semiconductor layer 118 of each of the epitaxial structures of the first and second source or drain structures includes silicon, germanium and boron, the germanium having an atomic concentration of less than 40% at the abrupt interface. The capping semiconductor layer 123 or 123′ of each of the epitaxial structures of the first and second source or drain structures includes silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% at the abrupt interface and throughout the capping semiconductor layer 123 or 123′.

In an embodiment, the capping semiconductor layer 123 or 123′ of each of the epitaxial structures of the first and second source or drain structures includes the germanium having an atomic concentration of greater than 55%. In an embodiment, the capping semiconductor layer 123 or 123′ of each of the epitaxial structures of the first and second source or drain structures includes the boron having an atomic concentration of greater than 9E20 cm⁻³. In an embodiment, the lower semiconductor layer 118 of each of the epitaxial structures of the first and second source or drain structures includes the germanium having an atomic concentration of less than 30%.

In an embodiment, the integrated circuit structure further includes a metal silicide layer 128A on and in direct contact with the capping semiconductor layer 123 or 123′ of each of the epitaxial structures of the first and second source or drain structures. In one embodiment, the metal silicide layer 128A is a silicide of a silicon germanium layer having a composition substantially the same as the composition of the capping semiconductor layer 123 or 123′. In one embodiment, the integrated circuit structure further includes a first conductive contact 128B/128C on a first portion of the metal silicide layer 128A on the capping semiconductor layer 123 or 123′ of the epitaxial structure of the first source or drain structure, and a second conductive contact 128B/128C on a second portion of the metal silicide 128A layer on the capping semiconductor layer 123 or 123′ of the epitaxial structure of the second source or drain structure. In an embodiment, the metal silicide layer 128A includes a metal selected from group consisting of nickel, titanium, platinum, and combination of two or more thereof.

In an embodiment, the lower fin portion 104A includes a portion of an underlying bulk single crystalline silicon substrate 102. In an embodiment, the integrated circuit structure further includes first and second dielectric gate sidewall spacers along the first and second sides of the gate stack, respectively.

A high germanium concentration capping layer such as described herein may be grown on or within planar, trigate, FinFET, nanowire, or nanoribbon structures with minimal modification to a baseline process flow. As another exemplary process flow, FIGS. 2A-2F illustrate cross-sectional views representing various operations in a method of fabricating an integrated circuit structure having source or drain structures with a high germanium concentration capping layer, in accordance with an embodiment of the present disclosure.

Referring to FIG. 2A, optionally, a channel material 204 is grown on a substrate 202, such as a silicon substrate. In an embodiment, the channel material 204 includes silicon. In an embodiment, the channel material 204 includes silicon and germanium. In an embodiment, the channel material 204 includes germanium. In an embodiment, the channel material 204 is a group III-V material. In other embodiments, a distinct channel material 204 is not formed, and the following described process operations are performed on a surface of substrate 202.

Referring to FIG. 2B, channel material 204 is patterned into fins 206. The patterning may form recesses 208 into substrate 202, as is depicted.

Referring to FIG. 2C, trenches between the fins 206 are filled with a shallow trench isolation material which is then polished and recessed to form isolation structures 210. The process may further involve deposition, patterning and recessing of a dielectric isolation barrier. The process continues with deposition and patterning of gate oxide material and gate electrode material (which may be a dummy gate oxide material and dummy gate electrode material), and the formation of gate spacers to form gate stack 212 and gate spacers 214.

Referring to FIG. 2D, fins 206 are etched adjacent sides of gate stack 212 at locations 218. The etching leaves channel regions 216 beneath gate stack 212.

Referring to FIG. 2E, source or drain structure formation involves growth of a lower source or drain material 220, and a capping semiconductor layer 222. In an embodiment, an abrupt interface is between the capping semiconductor layer 222 and the lower source or drain material 220. In an embodiment, the lower source or drain material 220 includes silicon, germanium and boron, the germanium having an atomic concentration of less than 40% at the abrupt interface. The capping semiconductor layer 222 includes silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% at the abrupt interface and throughout the capping semiconductor layer 222.

In an embodiment, the capping semiconductor layer 222 includes the germanium having an atomic concentration of greater than 55%. In an embodiment, the capping semiconductor layer 222 includes the boron having an atomic concentration of greater than 9E20 cm⁻³. In an embodiment, the lower source or drain material 220 includes the germanium having an atomic concentration of less than 30%.

In an embodiment, the capping semiconductor layer 222 is formed by first forming a layer consisting essentially of germanium and boron on the lower source or drain material 220. A layer having silicon and boron is then formed on the layer consisting essentially of germanium and boron. The layer having silicon and boron and the layer consisting essentially of germanium and boron are the subjected to melting and then recrystallizing to form the capping semiconductor layer 222 on the lower source or drain material 220.

Referring to FIG. 2F, an isolation material is formed on the source or drain structures of FIG. 2E. The isolation material is then patterned and recessed to expose the source or drain structures and to form secondary spacers 226 and trenches 228. In one embodiment, the recessing of the isolation material is performed using an etch process which stops on or partially into the capping semiconductor layer 222 where, in the latter case, a patterned source or drain capping semiconductor layer 222′ is formed.

It is to be appreciated that further process of the structure of FIG. 2F can include formation of a metal silicide layer formed from an upper portion of the capping semiconductor layer 222 or the patterned source or drain capping semiconductor layer 222′. Source or drain contact material deposition and patterning can then be performed to form conductive contacts on the metal silicide layer. In an embodiment, the metal silicide layer is in direct contact with a top surface of the capping semiconductor layer 222 or the patterned source or drain capping semiconductor layer 222′, e.g., in contact with a structure having a germanium atomic concentration of greater than 50%, and greater than 55% in some cases. It is to be appreciated that back end of line processing may then be performed.

In another aspect, FIG. 3A illustrates a plan view of a plurality of gate lines over a pair of semiconductor fins, in accordance with another embodiment of the present disclosure.

Referring to FIG. 3A, a plurality of active gate lines 304 is formed over a plurality of semiconductor fins 300. Dummy gate lines 306 are at the ends of the plurality of semiconductor fins 300. Spacings 308 between the gate lines 304/306 are locations where trench contacts may be located to provide conductive contacts to source or drain regions, such as source or drain regions 351, 352, 353, and 354. In an embodiment, the pattern of the plurality of gate lines 304/306 or the pattern of the plurality of semiconductor fins 300 is described as a grating structure. In one embodiment, the grating-like pattern includes the plurality of gate lines 304/306 and/or the pattern of the plurality of semiconductor fins 300 spaced at a constant pitch and having a constant width, or both.

FIG. 3B illustrates a cross-sectional view, taken along the a-a′ axis of FIG. 3A, in accordance with an embodiment of the present disclosure.

Referring to FIG. 3B, a plurality of active gate lines 364 is formed over a semiconductor fin 362 formed above a substrate 360. Dummy gate lines 366 are at the ends of the semiconductor fin 362. A dielectric layer 370 is outside of the dummy gate lines 366. A trench contact material 397 is between the active gate lines 364, and between the dummy gate lines 366 and the active gate lines 364. Embedded source or drain structures 368 and corresponding metal silicide layers 369 are in/on the semiconductor fin 362 between the active gate lines 364 and between the dummy gate lines 366 and the active gate lines 364. Embedded source or drain structures 368 and corresponding metal silicide layers 369 may be as described in association with the source or drain structures having a high germanium concentration capping layer and corresponding metal silicide layers described above in association with FIGS. 1A-1G and 2A-2F.

The active gate lines 364 include a gate dielectric structure 398/399, a workfunction gate electrode portion 374 and a fill gate electrode portion 376, and a dielectric capping layer 378. Dielectric spacers 380 line the sidewalls of the active gate lines 364 and the dummy gate lines 366.

In another aspect, trench contact structures, e.g., for source or drain regions, are described. In an example, FIG. 4 illustrates a cross-sectional view of an integrated circuit structure having trench contacts for a PMOS device, in accordance with another embodiment of the present disclosure.

Referring to FIG. 4, an integrated circuit structure 450 includes a fin 452, such as a silicon germanium fin. A gate dielectric layer 454 is over fin 452. A gate electrode 456 is over the gate dielectric layer 454. In an embodiment, the gate electrode 456 includes a conformal conductive layer 458 and a conductive fill 460. In an embodiment, a dielectric cap 462 is over the gate electrode 456 and over the gate dielectric layer 454. The gate electrode has a first side 456A and a second side 456B opposite the first side 456A. Dielectric spacers 463 are along the sidewalls of the gate electrode 456. In one embodiment, the gate dielectric layer 454 is further between a first of the dielectric spacers 463 and the first side 456A of the gate electrode 456, and between a second of the dielectric spacers 463 and the second side 456B of the gate electrode 456, as is depicted. In an embodiment, although not depicted, a thin oxide layer, such as a thermal or chemical silicon oxide or silicon dioxide layer, is between the fin 452 and the gate dielectric layer 454.

First 464 and second 466 epitaxial semiconductor source or drain structures are adjacent the first 456A and second 456B sides of the gate electrode 456, respectively. In one embodiment, the first 464 and second 466 epitaxial semiconductor source or drain structures include have a corresponding metal silicide layer 495 or 497 thereon, and are formed in recesses 465 and 467, respectively, of the fin 452, as is depicted. In an embodiment, the metal silicide layers 495 and 497 are in direct contact with a high germanium content (e.g., greater than 55 atomic percent) portion 482 of silicon germanium epitaxial source or drain structures 464 and 466. First 464 and second 466 epitaxial semiconductor source or drain structures and corresponding metal silicide layer 495 or 497 may be as described in association with the source or drain structures having a high germanium concentration capping layer and corresponding metal silicide layers described above in association with FIGS. 1A-1G and 2A-2F.

First 468 and second 470 trench contact structures are over the first 464 and second 466 semiconductor source or drain regions adjacent the first 456A and second 456B sides of the gate electrode 456, respectively. The first 468 and second 470 trench contact structures both include a U-shaped metal layer 472 and a T-shaped metal layer 474 on and over the entirety of the U-shaped metal layer 472. In one embodiment, the U-shaped metal layer 472 and the T-shaped metal layer 474 differ in composition. In one such embodiment, the U-shaped metal layer 472 includes titanium, and the T-shaped metal layer 474 includes cobalt. In one embodiment, the first 468 and second 470 trench contact structures both further include a third metal layer 476 on the T-shaped metal layer 474. In one such embodiment, the third metal layer 476 and the U-shaped metal layer 472 have a same composition. In a particular embodiment, the third metal layer 476 and the U-shaped metal layer 472 include titanium, and the T-shaped metal layer 474 includes cobalt.

A first trench contact via 478 is electrically connected to the first trench contact 468. In a particular embodiment, the first trench contact via 478 is on and coupled to the third metal layer 476 of the first trench contact 468. The first trench contact via 478 is further over and in contact with a portion of one of the dielectric spacers 463, and over and in contact with a portion of the dielectric cap 462. A second trench contact via 480 is electrically connected to the second trench contact 470. In a particular embodiment, the second trench contact via 480 is on and coupled to the third metal layer 476 of the second trench contact 470. The second trench contact via 480 is further over and in contact with a portion of another of the dielectric spacers 463, and over and in contact with another portion of the dielectric cap 462.

One or more embodiments described herein are directed to the use of metal chemical vapor deposition for wrap-around semiconductor contacts. Embodiments may be applicable to or include one or more of chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), conductive contact fabrication, or thin films. Particular embodiments may include the fabrication of a titanium or like metallic layer using a low temperature (e.g., less than 500 degrees Celsius, or in the range of 400-500 degrees Celsius) chemical vapor deposition of a contact metal to provide a conformal source or drain contact. Implementation of such a conformal source or drain contact may improve three-dimensional (3D) transistor complementary metal oxide semiconductor (CMOS) performance.

To provide context, metal to semiconductor contact layers may be deposited using sputtering. Sputtering is a line of sight process and may not be well suited to 3D transistor fabrication. Known sputtering solutions have poor or incomplete metal-semiconductor junctions on device contact surfaces with an angle to the incidence of deposition. In accordance with one or more embodiments of the present disclosure, a low temperature chemical vapor deposition process is implemented for fabrication of a contact metal to provide conformality in three dimensions and maximize the metal semiconductor junction contact area. The resulting greater contact area may reduce the resistance of the junction. Embodiments may include deposition on semiconductor surfaces having a non-flat topography, where the topography of an area refers to the surface shapes and features themselves, and a non-flat topography includes surface shapes and features or portions of surface shapes and features that are non-flat, i.e., surface shapes and features that are not entirely flat. In an embodiment, deposition is on a semiconductor surface of a source or drain structure having a relatively high germanium content.

Embodiments described herein may include fabrication of wrap-around contact structures. In one such embodiment, the use of pure metal conformally deposited onto transistor source-drain contacts by chemical vapor deposition, plasma enhanced chemical vapor deposition, atomic layer deposition, or plasma enhanced atomic layer deposition is described. Such conformal deposition may be used to increase the available area of metal semiconductor contact and reduce resistance, improving the performance of the transistor device. In an embodiment, the relatively low temperature of the deposition leads to a minimized resistance of the junction per unit area.

It is to be appreciated that a variety of integrated circuit structures may be fabricated using an integration scheme involving a metallic layer deposition process as described herein. In accordance with an embodiment of the present disclosure, a method of fabricating an integrated circuit structure includes providing a substrate in a chemical vapor deposition (CVD) chamber having an RF source, the substrate having a feature thereon. The method also includes reacting titanium tetrachloride (TiCl₄) and hydrogen (H₂) to form a titanium (Ti) layer on the feature of the substrate. In an embodiment, the titanium layer has a total atomic composition including 98% or greater of titanium and 0.5-2% of chlorine. In alternative embodiments, a similar process is used to fabricate a high purity metallic layer of zirconium (Zr), hafnium (Hf), tantalum (Ta), niobium (Nb), or vanadium (V).

In accordance with an embodiment of the present disclosure, the feature of the substrate is a source or drain contact trench exposing a semiconductor source or drain structure. The titanium layer (or other high purity metallic layer) is a conductive contact layer for the semiconductor source or drain structure. Exemplary embodiments of such an implementation are described below in association with FIG. 5.

FIG. 5 illustrates a cross-sectional view of an integrated circuit structure having a conductive contact on a raised source or drain region, in accordance with an embodiment of the present disclosure.

Referring to FIG. 5, a semiconductor structure 550 includes a gate structure 552 above a substrate 554. The gate structure 552 includes a gate dielectric layer 552A, a workfunction layer 552B, and a gate fill 552C. A source region 558 and a drain region 560 are on opposite sides of the gate structure 552. Source or drain contacts 562 are electrically connected to the source region 558 and the drain region 560, and are spaced apart of the gate structure 552 by one or both of an inter-layer dielectric layer 564 or gate dielectric spacers 566. The source region 558 and the drain region 560 are or include epitaxial or embedded material regions formed in etched-out regions of the substrate 554. A metal silicide layer 502 is formed thereon. The epitaxial or embedded material regions of the source region 558 and the drain region 560, and the metal silicide layer 502, may be as described in association with the source or drain structures having a high germanium concentration capping layer and corresponding metal silicide layers described above in association with FIGS. 1A-1G and 2A-2F.

In an embodiment, the source or drain contacts 562 include a high purity metallic layer 562A, such as described above, and a conductive trench fill material 562B. In one embodiment, the high purity metallic layer 562A has a total atomic composition including 98% or greater of titanium. In one such embodiment, the total atomic composition of the high purity metallic layer 562A further includes 0.5-2% of chlorine. In an embodiment, the high purity metallic layer 562A has a thickness variation of 30% or less. In an embodiment, the conductive trench fill material 562B is composed of a conductive material such as, but not limited to, Cu, Al, W, Co, or alloys thereof.

In another aspect, contact over active gate (COAG) structures and processes are described. One or more embodiments of the present disclosure are directed to semiconductor structures or devices having one or more gate contact structures (e.g., as gate contact vias) disposed over active portions of gate electrodes of the semiconductor structures or devices. One or more embodiments of the present disclosure are directed to methods of fabricating semiconductor structures or devices having one or more gate contact structures formed over active portions of gate electrodes of the semiconductor structures or devices. Approaches described herein may be used to reduce a standard cell area by enabling gate contact formation over active gate regions. In one or more embodiments, the gate contact structures fabricated to contact the gate electrodes are self-aligned via structures.

In an embodiment, an integrated circuit structure, semiconductor structure or device is a non-planar device such as, but not limited to, a fin-FET or a tri-gate device. In such an embodiment, a corresponding semiconducting channel region is composed of or is formed in a three-dimensional body. In one such embodiment, gate electrode stacks of gate lines surround at least a top surface and a pair of sidewalls of the three-dimensional body. In another embodiment, at least the channel region is made to be a discrete three-dimensional body, such as in a gate-all-around device (e.g., nanowire or nanoribbon). In one such embodiment, each gate electrode stack of a plurality of gate lines completely surrounds the channel region.

More generally, one or more embodiments are directed to approaches for, and structures formed from, landing a gate contact via directly on an active transistor gate. Such approaches may eliminate the need for extension of a gate line on isolation for contact purposes. Such approaches may also eliminate the need for a separate gate contact (GCN) layer to conduct signals from a gate line or structure. In an embodiment, eliminating the above features is achieved by recessing contact metals in a trench contact (TCN) and introducing an additional dielectric material in the process flow (e.g., TILA). The additional dielectric material is included as a trench contact dielectric cap layer with etch characteristics different from the gate dielectric material cap layer already used for trench contact alignment in a gate aligned contact process (GAP) processing scheme (e.g., GILA).

In an embodiment, providing an integrated circuit structure involves formation of a contact pattern which is essentially perfectly aligned to an existing gate pattern while eliminating the use of a lithographic operation with exceedingly tight registration budget. In one such embodiment, this approach enables the use of intrinsically highly selective wet etching (e.g., versus dry or plasma etching) to generate contact openings. In an embodiment, a contact pattern is formed by utilizing an existing gate pattern in combination with a contact plug lithography operation. In one such embodiment, the approach enables elimination of the need for an otherwise critical lithography operation to generate a contact pattern, as used in other approaches. In an embodiment, a trench contact grid is not separately patterned, but is rather formed between poly (gate) lines. For example, in one such embodiment, a trench contact grid is formed subsequent to gate grating patterning but prior to gate grating cuts.

Furthermore, gate stack structures may be fabricated by a replacement gate process. In such a scheme, dummy gate material such as polysilicon or silicon nitride pillar material, may be removed and replaced with permanent gate electrode material. In one such embodiment, a permanent gate dielectric layer is also formed in this process, as opposed to being carried through from earlier processing. In an embodiment, dummy gates are removed by a dry etch or wet etch process. In one embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a dry etch process including SF₆. In another embodiment, dummy gates are composed of polycrystalline silicon or amorphous silicon and are removed with a wet etch process including aqueous NH₄OH or tetramethylammonium hydroxide. In one embodiment, dummy gates are composed of silicon nitride and are removed with a wet etch including aqueous phosphoric acid.

In an embodiment, one or more approaches described herein contemplate essentially a dummy and replacement gate process in combination with a dummy and replacement contact process to arrive at an integrated circuit structure. In one such embodiment, the replacement contact process is performed after the replacement gate process to allow high temperature anneal of at least a portion of the permanent gate stack. For example, in a specific such embodiment, an anneal of at least a portion of the permanent gate structures, e.g., after a gate dielectric layer is formed, is performed at a temperature greater than approximately 600 degrees Celsius. The anneal is performed prior to formation of the permanent contacts.

It is to be appreciated that differing structural relationships between an insulating gate cap layer and an insulating trench contact cap layer may be fabricated. As examples, FIGS. 6A and 6B illustrate cross-sectional views of various integrated circuit structures, each having trench contacts including an overlying insulating cap layer and having gate stacks including an overlying insulating cap layer, in accordance with an embodiment of the present disclosure.

Referring to FIGS. 6A and 6B, integrated circuit structures 600A and 600B, respectively, include a fin 602, such as a silicon germanium fin. Although depicted as a cross-sectional view, it is to be appreciated that the fin 602 has a top 602A and sidewalls (into and out of the page of the perspective shown). First 604 and second 606 gate dielectric layers are over the top 602A of the fin 602 and laterally adjacent the sidewalls of the fin 602. First 608 and second 610 gate electrodes are over the first 604 and second 606 gate dielectric layers, respectively, over the top 602A of the fin 602 and laterally adjacent the sidewalls of the fin 602. The first 608 and second 610 gate electrodes each include a conformal conductive layer 609A, such as a workfunction-setting layer, and a conductive fill material 609B above the conformal conductive layer 609A. The first 608 and second 610 gate electrodes both have a first side 612 and a second side 614 opposite the first side 612. The first 608 and second 610 gate electrodes also both have an insulating cap 616 having a top surface 618.

A first dielectric spacer 620 is adjacent the first side 612 of the first gate electrode 608. A second dielectric spacer 622 is adjacent the second side 614 of the second gate electrode 610. A semiconductor source or drain region 624 is adjacent the first 620 and second 622 dielectric spacers. A trench contact structure 626 is over the semiconductor source or drain region 624 adjacent the first 620 and second 622 dielectric spacers. In an embodiment, the semiconductor source or drain region 624 has a structure such as described above in association with FIG. 1A-1G or 2A-2F, and other embodiments described herein.

The trench contact structure 626 includes an insulating cap 628 on a conductive structure 630. The insulating cap 628 of the trench contact structure 626 has a top surface 629 substantially co-planar with a top surfaces 618 of the insulating caps 616 of the first 608 and second 610 gate electrodes. In an embodiment, the insulating cap 628 of the trench contact structure 626 extends laterally into recesses 632 in the first 620 and second 622 dielectric spacers. In such an embodiment, the insulating cap 628 of the trench contact structure 626 overhangs the conductive structure 630 of the trench contact structure 626. In other embodiments, however, the insulating cap 628 of the trench contact structure 626 does not extend laterally into recesses 632 in the first 620 and second 622 dielectric spacers and, hence, does not overhang the conductive structure 630 of the trench contact structure 626.

It is to be appreciated that the conductive structure 630 of the trench contact structure 626 may not be rectangular, as depicted in FIGS. 6A and 6B. For example, the conductive structure 630 of the trench contact structure 626 may have a cross-sectional geometry similar to or the same as the geometry shown for conductive structure 630A illustrated in the projection of FIG. 6A.

In an embodiment, the insulating cap 628 of the trench contact structure 626 has a composition different than a composition of the insulating caps 616 of the first 608 and second 610 gate electrodes. In one such embodiment, the insulating cap 628 of the trench contact structure 626 includes a carbide material, such as a silicon carbide material. The insulating caps 616 of the first 608 and second 610 gate electrodes include a nitride material, such as a silicon nitride material.

In an embodiment, the insulating caps 616 of the first 608 and second 610 gate electrodes both have a bottom surface 617A below a bottom surface 628A of the insulating cap 628 of the trench contact structure 626, as is depicted in FIG. 6A. In another embodiment, the insulating caps 616 of the first 608 and second 610 gate electrodes both have a bottom surface 617B substantially co-planar with a bottom surface 628B of the insulating cap 628 of the trench contact structure 626, as is depicted in FIG. 6B. In another embodiment, although not depicted, the insulating caps 616 of the first 608 and second 610 gate electrodes both have a bottom surface above a bottom surface of an insulating cap 628 of a trench contact structure 626.

In an embodiment, the conductive structure 630 of the trench contact structure 626 includes a U-shaped metal layer 634, a T-shaped metal layer 636 on and over the entirety of the U-shaped metal layer 634, and a third metal layer 638 on the T-shaped metal layer 636. The insulating cap 628 of the trench contact structure 626 is on the third metal layer 638. In one such embodiment, the third metal layer 638 and the U-shaped metal layer 634 include titanium, and the T-shaped metal layer 636 includes cobalt. In a particular such embodiment, the T-shaped metal layer 636 further includes carbon.

In an embodiment, a metal silicide layer 640 is directly between the conductive structure 630 of the trench contact structure 626 and the semiconductor source or drain region 624. In one such embodiment, the metal silicide layer 640 includes nickel, platinum, germanium and silicon. In a particular embodiment, the semiconductor source or drain region 624 is a P-type semiconductor source or drain region.

As described throughout the present application, a substrate may be composed of a semiconductor material that can withstand a manufacturing process and in which charge can migrate. In an embodiment, a substrate is described herein is a bulk substrate composed of a crystalline silicon, silicon/germanium or germanium layer doped with a charge carrier, such as but not limited to phosphorous, arsenic, boron or a combination thereof, to form an active region. In one embodiment, the concentration of silicon atoms in such a bulk substrate is greater than 97%. In another embodiment, a bulk substrate is composed of an epitaxial layer grown atop a distinct crystalline substrate, e.g. a silicon epitaxial layer grown atop a boron-doped bulk silicon mono-crystalline substrate. A bulk substrate may alternatively be composed of a group III-V material. In an embodiment, a bulk substrate is composed of a group III-V material such as, but not limited to, gallium nitride, gallium phosphide, gallium arsenide, indium phosphide, indium antimonide, indium gallium arsenide, aluminum gallium arsenide, indium gallium phosphide, or a combination thereof. In one embodiment, a bulk substrate is composed of a group III-V material and the charge-carrier dopant impurity atoms are ones such as, but not limited to, carbon, silicon, germanium, oxygen, sulfur, selenium or tellurium.

As described throughout the present application, isolation regions such as shallow trench isolation regions or sub-fin isolation regions may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, portions of a permanent gate structure from an underlying bulk substrate or to isolate active regions formed within an underlying bulk substrate, such as isolating fin active regions. For example, in one embodiment, an isolation region is composed of one or more layers of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, carbon-doped silicon nitride, or a combination thereof.

As described throughout the present application, gate lines or gate structures may be composed of a gate electrode stack which includes a gate dielectric layer and a gate electrode layer. In an embodiment, the gate electrode of the gate electrode stack is composed of a metal gate and the gate dielectric layer is composed of a high-k material. For example, in one embodiment, the gate dielectric layer is composed of a material such as, but not limited to, hafnium oxide, hafnium oxy-nitride, hafnium silicate, lanthanum oxide, zirconium oxide, zirconium silicate, tantalum oxide, barium strontium titanate, barium titanate, strontium titanate, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, lead zinc niobate, or a combination thereof. Furthermore, a portion of gate dielectric layer may include a layer of native oxide formed from the top few layers of a semiconductor substrate. In an embodiment, the gate dielectric layer is composed of a top high-k portion and a lower portion composed of an oxide of a semiconductor material. In one embodiment, the gate dielectric layer is composed of a top portion of hafnium oxide and a bottom portion of silicon dioxide or silicon oxy-nitride. In some implementations, a portion of the gate dielectric is a “U”-shaped structure that includes a bottom portion substantially parallel to the surface of the substrate and two sidewall portions that are substantially perpendicular to the top surface of the substrate.

In one embodiment, a gate electrode is composed of a metal layer such as, but not limited to, metal nitrides, metal carbides, metal silicides, metal aluminides, hafnium, zirconium, titanium, tantalum, aluminum, ruthenium, palladium, platinum, cobalt, nickel or conductive metal oxides. In a specific embodiment, the gate electrode is composed of a non-workfunction-setting fill material formed above a metal workfunction-setting layer. The gate electrode layer may consist of a P-type workfunction metal or an N-type workfunction metal, depending on whether the transistor is to be a PMOS or an NMOS transistor. In some implementations, the gate electrode layer may consist of a stack of two or more metal layers, where one or more metal layers are workfunction metal layers and at least one metal layer is a conductive fill layer. For a PMOS transistor, metals that may be used for the gate electrode include, but are not limited to, ruthenium, palladium, platinum, cobalt, nickel, and conductive metal oxides, e.g., ruthenium oxide. A P-type metal layer will enable the formation of a PMOS gate electrode with a workfunction that is between about 4.9 eV and about 5.2 eV. For an NMOS transistor, metals that may be used for the gate electrode include, but are not limited to, hafnium, zirconium, titanium, tantalum, aluminum, alloys of these metals, and carbides of these metals such as hafnium carbide, zirconium carbide, titanium carbide, tantalum carbide, and aluminum carbide. An N-type metal layer will enable the formation of an NMOS gate electrode with a workfunction that is between about 3.9 eV and about 4.2 eV. In some implementations, the gate electrode may consist of a “U”-shaped structure that includes a bottom portion substantially parallel to the surface of the substrate and two sidewall portions that are substantially perpendicular to the top surface of the substrate. In another implementation, at least one of the metal layers that form the gate electrode may simply be a planar layer that is substantially parallel to the top surface of the substrate and does not include sidewall portions substantially perpendicular to the top surface of the substrate. In further implementations of the disclosure, the gate electrode may consist of a combination of U-shaped structures and planar, non-U-shaped structures. For example, the gate electrode may consist of one or more U-shaped metal layers formed atop one or more planar, non-U-shaped layers.

As described throughout the present application, spacers associated with gate lines or electrode stacks may be composed of a material suitable to ultimately electrically isolate, or contribute to the isolation of, a permanent gate structure from adjacent conductive contacts, such as self-aligned contacts. For example, in one embodiment, the spacers are composed of a dielectric material such as, but not limited to, silicon dioxide, silicon oxy-nitride, silicon nitride, or carbon-doped silicon nitride.

In an embodiment, approaches described herein may involve formation of a contact pattern which is very well aligned to an existing gate pattern while eliminating the use of a lithographic operation with exceedingly tight registration budget. In one such embodiment, this approach enables the use of intrinsically highly selective wet etching (e.g., versus dry or plasma etching) to generate contact openings. In an embodiment, a contact pattern is formed by utilizing an existing gate pattern in combination with a contact plug lithography operation. In one such embodiment, the approach enables elimination of the need for an otherwise critical lithography operation to generate a contact pattern, as used in other approaches. In an embodiment, a trench contact grid is not separately patterned, but is rather formed between poly (gate) lines. For example, in one such embodiment, a trench contact grid is formed subsequent to gate grating patterning but prior to gate grating cuts.

Pitch division processing and patterning schemes may be implemented to enable embodiments described herein or may be included as part of embodiments described herein. Pitch division patterning typically refers to pitch halving, pitch quartering etc. Pitch division schemes may be applicable to FEOL processing, BEOL processing, or both FEOL (device) and BEOL (metallization) processing. In accordance with one or more embodiments described herein, optical lithography is first implemented to print unidirectional lines (e.g., either strictly unidirectional or predominantly unidirectional) in a pre-defined pitch. Pitch division processing is then implemented as a technique to increase line density.

In an embodiment, the term “grating structure” for fins, gate lines, metal lines, ILD lines or hardmask lines is used herein to refer to a tight pitch grating structure. In one such embodiment, the tight pitch is not achievable directly through a selected lithography. For example, a pattern based on a selected lithography may first be formed, but the pitch may be halved by the use of spacer mask patterning, as is known in the art. Even further, the original pitch may be quartered by a second round of spacer mask patterning. Accordingly, the grating-like patterns described herein may have metal lines, ILD lines or hardmask lines spaced at a substantially consistent pitch and having a substantially consistent width. For example, in some embodiments the pitch variation would be within ten percent and the width variation would be within ten percent, and in some embodiments, the pitch variation would be within five percent and the width variation would be within five percent. The pattern may be fabricated by a pitch halving or pitch quartering, or other pitch division, approach. In an embodiment, the grating is not necessarily single pitch.

In an embodiment, as used throughout the present description, interlayer dielectric (ILD) material is composed of or includes a layer of a dielectric or insulating material. Examples of suitable dielectric materials include, but are not limited to, oxides of silicon (e.g., silicon dioxide (SiO₂)), doped oxides of silicon, fluorinated oxides of silicon, carbon doped oxides of silicon, various low-k dielectric materials known in the arts, and combinations thereof. The interlayer dielectric material may be formed by techniques, such as, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), or by other deposition methods.

In an embodiment, as is also used throughout the present description, metal lines or interconnect line material (and via material) is composed of one or more metal or other conductive structures. A common example is the use of copper lines and structures that may or may not include barrier layers between the copper and surrounding ILD material. As used herein, the term metal includes alloys, stacks, and other combinations of multiple metals. For example, the metal interconnect lines may include barrier layers (e.g., layers including one or more of Ta, TaN, Ti or TiN), stacks of different metals or alloys, etc. Thus, the interconnect lines may be a single material layer, or may be formed from several layers, including conductive liner layers and fill layers. Any suitable deposition process, such as electroplating, chemical vapor deposition or physical vapor deposition, may be used to form interconnect lines. In an embodiment, the interconnect lines are composed of a conductive material such as, but not limited to, Cu, Al, Ti, Zr, Hf, V, Ru, Co, Ni, Pd, Pt, W, Ag, Au or alloys thereof. The interconnect lines are also sometimes referred to in the art as traces, wires, lines, metal, or simply interconnect.

In an embodiment, as is also used throughout the present description, hardmask materials are composed of dielectric materials different from the interlayer dielectric material. In one embodiment, different hardmask materials may be used in different regions so as to provide different growth or etch selectivity to each other and to the underlying dielectric and metal layers. In some embodiments, a hardmask layer includes a layer of a nitride of silicon (e.g., silicon nitride) or a layer of an oxide of silicon, or both, or a combination thereof. Other suitable materials may include carbon-based materials. In another embodiment, a hardmask material includes a metal species. For example, a hardmask or other overlying material may include a layer of a nitride of titanium or another metal (e.g., titanium nitride). Potentially lesser amounts of other materials, such as oxygen, may be included in one or more of these layers. Alternatively, other hardmask layers known in the arts may be used depending upon the particular implementation. The hardmask layers maybe formed by CVD, PVD, or by other deposition methods.

In an embodiment, as is also used throughout the present description, lithographic operations are performed using 193 nm immersion lithography (i193), extreme ultra-violet (EUV) lithography or electron beam direct write (EBDW) lithography, or the like. A positive tone or a negative tone resist may be used. In one embodiment, a lithographic mask is a trilayer mask composed of a topographic masking portion, an anti-reflective coating (ARC) layer, and a photoresist layer. In a particular such embodiment, the topographic masking portion is a carbon hardmask (CHM) layer and the anti-reflective coating layer is a silicon ARC layer.

It is to be appreciated that not all aspects of the processes described above need be practiced to fall within the spirit and scope of embodiments of the present disclosure. For example, in one embodiment, dummy gates need not ever be formed prior to fabricating gate contacts over active portions of the gate stacks. The gate stacks described above may actually be permanent gate stacks as initially formed. Also, the processes described herein may be used to fabricate one or a plurality of semiconductor devices. The semiconductor devices may be transistors or like devices. For example, in an embodiment, the semiconductor devices are a metal-oxide semiconductor (MOS) transistors for logic or memory, or are bipolar transistors. Also, in an embodiment, the semiconductor devices have a three-dimensional architecture, such as a trigate device, an independently accessed double gate device, a FIN-FET, a nanowire device, or a nanoribbon device. One or more embodiments may be particularly useful for fabricating semiconductor devices at a 10 nanometer (10 nm) technology node sub-10 nanometer (10 nm) technology node.

Additional or intermediate operations for FEOL layer or structure fabrication may include standard microelectronic fabrication processes such as lithography, etch, thin films deposition, planarization (such as chemical mechanical polishing (CMP)), diffusion, metrology, the use of sacrificial layers, the use of etch stop layers, the use of planarization stop layers, or any other associated action with microelectronic component fabrication. Also, it is to be appreciated that the process operations described for the preceding process flows may be practiced in alternative sequences, not every operation need be performed or additional process operations may be performed, or both.

It is to be appreciated that in the above exemplary FEOL embodiments, in an embodiment, 10 nanometer or sub-10 nanometer node processing is implemented directly in to the fabrication schemes and resulting structures as a technology driver. In other embodiment, FEOL considerations may be driven by BEOL 10 nanometer or sub-10 nanometer processing requirements. For example, material selection and layouts for FEOL layers and devices may need to accommodate BEOL processing. In one such embodiment, material selection and gate stack architectures are selected to accommodate high density metallization of the BEOL layers, e.g., to reduce fringe capacitance in transistor structures formed in the FEOL layers but coupled together by high density metallization of the BEOL layers.

Embodiments disclosed herein may be used to manufacture a wide variety of different types of integrated circuits or microelectronic devices. Examples of such integrated circuits include, but are not limited to, processors, chipset components, graphics processors, digital signal processors, micro-controllers, and the like. In other embodiments, semiconductor memory may be manufactured. Moreover, the integrated circuits or other microelectronic devices may be used in a wide variety of electronic devices known in the arts. For example, in computer systems (e.g., desktop, laptop, server), cellular phones, personal electronics, etc. The integrated circuits may be coupled with a bus and other components in the systems. For example, a processor may be coupled by one or more buses to a memory, a chipset, etc. Each of the processor, the memory, and the chipset, may potentially be manufactured using the approaches disclosed herein.

FIG. 7 illustrates a computing device 700 in accordance with one implementation of the disclosure. The computing device 700 houses a board 702. The board 702 may include a number of components, including but not limited to a processor 704 and at least one communication chip 706. The processor 704 is physically and electrically coupled to the board 702. In some implementations the at least one communication chip 706 is also physically and electrically coupled to the board 702. In further implementations, the communication chip 706 is part of the processor 704.

Depending on its applications, computing device 700 may include other components that may or may not be physically and electrically coupled to the board 702. These other components include, but are not limited to, volatile memory (e.g., DRAM), non-volatile memory (e.g., ROM), flash memory, a graphics processor, a digital signal processor, a crypto processor, a chipset, an antenna, a display, a touchscreen display, a touchscreen controller, a battery, an audio codec, a video codec, a power amplifier, a global positioning system (GPS) device, a compass, an accelerometer, a gyroscope, a speaker, a camera, and a mass storage device (such as hard disk drive, compact disk (CD), digital versatile disk (DVD), and so forth).

The communication chip 706 enables wireless communications for the transfer of data to and from the computing device 700. The term “wireless” and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. The communication chip 706 may implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. The computing device 700 may include a plurality of communication chips 706. For instance, a first communication chip 706 may be dedicated to shorter range wireless communications such as Wi-Fi and Bluetooth and a second communication chip 706 may be dedicated to longer range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others.

The processor 704 of the computing device 700 includes an integrated circuit die packaged within the processor 704. In some implementations of embodiments of the disclosure, the integrated circuit die of the processor includes one or more structures, such as integrated circuit structures built in accordance with implementations of the disclosure. The term “processor” may refer to any device or portion of a device that processes electronic data from registers or memory to transform that electronic data, or both, into other electronic data that may be stored in registers or memory, or both.

The communication chip 706 also includes an integrated circuit die packaged within the communication chip 706. In accordance with another implementation of the disclosure, the integrated circuit die of the communication chip is built in accordance with implementations of the disclosure.

In further implementations, another component housed within the computing device 700 may contain an integrated circuit die built in accordance with implementations of embodiments of the disclosure.

In various embodiments, the computing device 700 may be a laptop, a netbook, a notebook, an ultrabook, a smartphone, a tablet, a personal digital assistant (PDA), an ultramobile PC, a mobile phone, a desktop computer, a server, a printer, a scanner, a monitor, a set-top box, an entertainment control unit, a digital camera, a portable music player, or a digital video recorder. In further implementations, the computing device 700 may be any other electronic device that processes data.

FIG. 8 illustrates an interposer 800 that includes one or more embodiments of the disclosure. The interposer 800 is an intervening substrate used to bridge a first substrate 802 to a second substrate 804. The first substrate 802 may be, for instance, an integrated circuit die. The second substrate 804 may be, for instance, a memory module, a computer motherboard, or another integrated circuit die. Generally, the purpose of an interposer 800 is to spread a connection to a wider pitch or to reroute a connection to a different connection. For example, an interposer 800 may couple an integrated circuit die to a ball grid array (BGA) 806 that can subsequently be coupled to the second substrate 804. In some embodiments, the first and second substrates 802/804 are attached to opposing sides of the interposer 800. In other embodiments, the first and second substrates 802/804 are attached to the same side of the interposer 800. And, in further embodiments, three or more substrates are interconnected by way of the interposer 800.

The interposer 800 may be formed of an epoxy resin, a fiberglass-reinforced epoxy resin, a ceramic material, or a polymer material such as polyimide. In further implementations, the interposer 800 may be formed of alternate rigid or flexible materials that may include the same materials described above for use in a semiconductor substrate, such as silicon, germanium, and other group III-V and group IV materials.

The interposer 800 may include metal interconnects 808 and vias 810, including but not limited to through-silicon vias (TSVs) 812. The interposer 800 may further include embedded devices 814, including both passive and active devices. Such devices include, but are not limited to, capacitors, decoupling capacitors, resistors, inductors, fuses, diodes, transformers, sensors, and electrostatic discharge (ESD) devices. More complex devices such as radio-frequency (RF) devices, power amplifiers, power management devices, antennas, arrays, sensors, and MEMS devices may also be formed on the interposer 800. In accordance with embodiments of the disclosure, apparatuses or processes disclosed herein may be used in the fabrication of interposer 800 or in the fabrication of components included in the interposer 800.

FIG. 9 is an isometric view of a mobile computing platform 900 employing an integrated circuit (IC) fabricated according to one or more processes described herein or including one or more features described herein, in accordance with an embodiment of the present disclosure.

The mobile computing platform 900 may be any portable device configured for each of electronic data display, electronic data processing, and wireless electronic data transmission. For example, mobile computing platform 900 may be any of a tablet, a smart phone, laptop computer, etc. and includes a display screen 905 which in the exemplary embodiment is a touchscreen (capacitive, inductive, resistive, etc.), a chip-level (SoC) or package-level integrated system 910, and a battery 913. As illustrated, the greater the level of integration in the system 910 enabled by higher transistor packing density, the greater the portion of the mobile computing platform 900 that may be occupied by the battery 913 or non-volatile storage, such as a solid state drive, or the greater the transistor gate count for improved platform functionality. Similarly, the greater the carrier mobility of each transistor in the system 910, the greater the functionality. As such, techniques described herein may enable performance and form factor improvements in the mobile computing platform 900.

The integrated system 910 is further illustrated in the expanded view 920. In the exemplary embodiment, packaged device 977 includes at least one memory chip (e.g., RAM), or at least one processor chip (e.g., a multi-core microprocessor and/or graphics processor) fabricated according to one or more processes described herein or including one or more features described herein. The packaged device 977 is further coupled to the board 960 along with one or more of a power management integrated circuit (PMIC) 915, RF (wireless) integrated circuit (RFIC) 925 including a wideband RF (wireless) transmitter and/or receiver (e.g., including a digital baseband and an analog front end module further includes a power amplifier on a transmit path and a low noise amplifier on a receive path), and a controller thereof 911. Functionally, the PMIC 915 performs battery power regulation, DC-to-DC conversion, etc., and so has an input coupled to the battery 913 and with an output providing a current supply to all the other functional modules. As further illustrated, in the exemplary embodiment, the RFIC 925 has an output coupled to an antenna to provide to implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. In alternative implementations, each of these board-level modules may be integrated onto separate ICs coupled to the package substrate of the packaged device 977 or within a single IC (SoC) coupled to the package substrate of the packaged device 977.

In another aspect, semiconductor packages are used for protecting an integrated circuit (IC) chip or die, and also to provide the die with an electrical interface to external circuitry. With the increasing demand for smaller electronic devices, semiconductor packages are designed to be even more compact and must support larger circuit density. Furthermore, the demand for higher performance devices results in a need for an improved semiconductor package that enables a thin packaging profile and low overall warpage compatible with subsequent assembly processing.

In an embodiment, wire bonding to a ceramic or organic package substrate is used. In another embodiment, a C4 process is used to mount a die to a ceramic or organic package substrate. In particular, C4 solder ball connections can be implemented to provide flip chip interconnections between semiconductor devices and substrates. A flip chip or Controlled Collapse Chip Connection (C4) is a type of mounting used for semiconductor devices, such as integrated circuit (IC) chips, MEMS or components, which utilizes solder bumps instead of wire bonds. The solder bumps are deposited on the C4 pads, located on the top side of the substrate package. In order to mount the semiconductor device to the substrate, it is flipped over with the active side facing down on the mounting area. The solder bumps are used to connect the semiconductor device directly to the substrate.

FIG. 10 illustrates a cross-sectional view of a flip-chip mounted die, in accordance with an embodiment of the present disclosure.

Referring to FIG. 10, an apparatus 1000 includes a die 1002 such as an integrated circuit (IC) fabricated according to one or more processes described herein or including one or more features described herein, in accordance with an embodiment of the present disclosure. The die 1002 includes metallized pads 1004 thereon. A package substrate 1006, such as a ceramic or organic substrate, includes connections 1008 thereon. The die 1002 and package substrate 1006 are electrically connected by solder balls 1010 coupled to the metallized pads 1004 and the connections 1008. An underfill material 1012 surrounds the solder balls 1010.

Processing a flip chip may be similar to conventional IC fabrication, with a few additional operations. Near the end of the manufacturing process, the attachment pads are metalized to make them more receptive to solder. This typically consists of several treatments. A small dot of solder is then deposited on each metalized pad. The chips are then cut out of the wafer as normal. To attach the flip chip into a circuit, the chip is inverted to bring the solder dots down onto connectors on the underlying electronics or circuit board. The solder is then re-melted to produce an electrical connection, typically using an ultrasonic or alternatively reflow solder process. This also leaves a small space between the chip's circuitry and the underlying mounting. In most cases an electrically-insulating adhesive is then “underfilled” to provide a stronger mechanical connection, provide a heat bridge, and to ensure the solder joints are not stressed due to differential heating of the chip and the rest of the system.

In other embodiments, newer packaging and die-to-die interconnect approaches, such as through silicon via (TSV) and silicon interposer, are implemented to fabricate high performance Multi-Chip Module (MCM) and System in Package (SiP) incorporating an integrated circuit (IC) fabricated according to one or more processes described herein or including one or more features described herein, in accordance with an embodiment of the present disclosure.

Thus, embodiments of the present disclosure include integrated circuit structures having source or drain structures with a high germanium concentration capping layer, and methods of fabricating integrated circuit structures having source or drain structures with a high germanium concentration capping layer, are described.

Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of the present disclosure.

The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be formulated during prosecution of the present application (or an application claiming priority thereto) to any such combination of features. In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.

The following examples pertain to further embodiments. The various features of the different embodiments may be variously combined with some features included and others excluded to suit a variety of different applications.

Example embodiment 1: An integrated circuit structure includes a fin having a lower fin portion and an upper fin portion. A gate stack is over the upper fin portion of the fin, the gate stack having a first side opposite a second side. A first source or drain structure includes an epitaxial structure embedded in the fin at the first side of the gate stack, the epitaxial structure having a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer. A second source or drain structure includes an epitaxial structure embedded in the fin at the second side of the gate stack, the epitaxial structure having a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer. The lower semiconductor layer of each of the epitaxial structures of the first and second source or drain structures includes silicon, germanium and boron, the germanium having an atomic concentration of less than 40% at the abrupt interface. The capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures includes silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% at the abrupt interface and throughout the capping semiconductor layer.

Example embodiment 2: The integrated circuit structure of example embodiment 1, wherein the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures includes the germanium having an atomic concentration of greater than 55%.

Example embodiment 3: The integrated circuit structure of example embodiment 1 or 2, wherein the lower semiconductor layer of each of the epitaxial structures of the first and second source or drain structures includes the germanium having an atomic concentration of less than 30%.

Example embodiment 4: The integrated circuit structure of example embodiment 1, 2 or 3, wherein the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures includes the boron having an atomic concentration of greater than 9E20 cm⁻³.

Example embodiment 5: The integrated circuit structure of example embodiment 1, 2, 3 or 4, further including a metal silicide layer on and in direct contact with the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures.

Example embodiment 6: The integrated circuit structure of example embodiment 5, wherein the metal silicide layer is a silicide of a silicon germanium layer having a composition substantially the same as the composition of the capping semiconductor layer.

Example embodiment 7: The integrated circuit structure of example embodiment 5 or 6, further including a first conductive contact on a first portion of the metal silicide layer on the capping semiconductor layer of the epitaxial structure of the first source or drain structure, and a second conductive contact on a second portion of the metal silicide layer on the capping semiconductor layer of the epitaxial structure of the second source or drain structure.

Example embodiment 8: The integrated circuit structure of example embodiment 1, 2, 3, 4, 5, 6 or 7, wherein the lower fin portion includes a portion of an underlying bulk single crystalline silicon substrate.

Example embodiment 9: The integrated circuit structure of example embodiment 1, 2, 3, 4, 5, 6, 7 or 8, further including first and second dielectric gate sidewall spacers along the first and second sides of the gate stack, respectively.

Example embodiment 10: A method of fabricating an integrated circuit structure includes forming a fin having a lower fin portion and an upper fin portion. The method also includes forming a gate stack over the upper fin portion of the fin, the gate stack having a first side opposite a second side. The method also includes forming a first trench in the fin at the first side of the gate stack and forming a second trench in the fin at the second side of the gate stack. The method also includes forming a lower semiconductor layer in the first trench and in the second trench, wherein the lower semiconductor layer includes silicon, germanium and boron, the germanium having an atomic concentration of less than 40%. The method also includes forming a layer consisting essentially of germanium and boron on the lower semiconductor layer. The method also includes forming a layer having silicon and boron on the layer consisting essentially of germanium and boron. The method also includes melting and then recrystallizing the layer having silicon and boron and the layer consisting essentially of germanium and boron to form a capping semiconductor layer on the lower semiconductor layer.

Example embodiment 11: The method of example embodiment 10, wherein the capping semiconductor layer includes silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% throughout the capping semiconductor layer.

Example embodiment 12: The method of example embodiment 10 or 11, wherein the lower semiconductor layer includes the germanium having an atomic concentration of less than 30%.

Example embodiment 13: The method of example embodiment 10, 11 or 12, wherein the capping semiconductor layer includes the boron having an atomic concentration of greater than 9E20 cm⁻³.

Example embodiment 14: The method of example embodiment 10, 11, 12 or 13, further including forming a metal silicide layer on and in direct contact with the capping semiconductor layer.

Example embodiment 15: The method of example embodiment 14, wherein the metal silicide layer is a silicide of a silicon germanium layer having a composition substantially the same as the composition of the capping semiconductor layer.

Example embodiment 16: A computing device includes a board and a component coupled to the board. The component includes an integrated circuit structure. The integrated circuit structure includes a fin having a lower fin portion and an upper fin portion. A gate stack is over the upper fin portion of the fin, the gate stack having a first side opposite a second side. A first source or drain structure includes an epitaxial structure embedded in the fin at the first side of the gate stack, the epitaxial structure having a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer. A second source or drain structure includes an epitaxial structure embedded in the fin at the second side of the gate stack, the epitaxial structure having a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer. The lower semiconductor layer of each of the epitaxial structures of the first and second source or drain structures includes silicon, germanium and boron, the germanium having an atomic concentration of less than 40% at the abrupt interface. The capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures includes silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% at the abrupt interface and throughout the capping semiconductor layer.

Example embodiment 17: The computing device of example embodiment 16, further including a memory coupled to the board.

Example embodiment 18: The computing device of example embodiment 16 or 17, further including a communication chip coupled to the board.

Example embodiment 19: The computing device of example embodiment 16, 17 or 18, further including a camera coupled to the board.

Example embodiment 20: The computing device of example embodiment 16, 17, 18 or 19, further including a battery coupled to the board.

Example embodiment 21: The computing device of example embodiment 16, 17, 18, 19 or 20, further including an antenna coupled to the board.

Example embodiment 22: The computing device of example embodiment 16, 27, 18, 19, 20 or 21, wherein the component is a packaged integrated circuit die. 

What is claimed is:
 1. An integrated circuit structure, comprising: a fin having a lower fin portion and an upper fin portion; a gate stack over the upper fin portion of the fin, the gate stack having a first side opposite a second side; a first source or drain structure comprising an epitaxial structure embedded in the fin at the first side of the gate stack, the epitaxial structure comprising a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer; and a second source or drain structure comprising an epitaxial structure embedded in the fin at the second side of the gate stack, the epitaxial structure comprising a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer, wherein the lower semiconductor layer of each of the epitaxial structures of the first and second source or drain structures comprises silicon, germanium and boron, the germanium having an atomic concentration of less than 40% at the abrupt interface, and wherein the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures comprises silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% at the abrupt interface and throughout the capping semiconductor layer.
 2. The integrated circuit structure of claim 1, wherein the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures comprises the germanium having an atomic concentration of greater than 55%.
 3. The integrated circuit structure of claim 1, wherein the lower semiconductor layer of each of the epitaxial structures of the first and second source or drain structures comprises the germanium having an atomic concentration of less than 30%.
 4. The integrated circuit structure of claim 1, wherein the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures comprises the boron having an atomic concentration of greater than 9E20 cm⁻³.
 5. The integrated circuit structure of claim 1, further comprising: a metal silicide layer on and in direct contact with the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures.
 6. The integrated circuit structure of claim 5, wherein the metal silicide layer is a silicide of a silicon germanium layer having a composition substantially the same as the composition of the capping semiconductor layer.
 7. The integrated circuit structure of claim 5, further comprising: a first conductive contact on a first portion of the metal silicide layer on the capping semiconductor layer of the epitaxial structure of the first source or drain structure; and a second conductive contact on a second portion of the metal silicide layer on the capping semiconductor layer of the epitaxial structure of the second source or drain structure.
 8. The integrated circuit structure of claim 1, wherein the lower fin portion includes a portion of an underlying bulk single crystalline silicon substrate.
 9. The integrated circuit structure of claim 1, further comprising: first and second dielectric gate sidewall spacers along the first and second sides of the gate stack, respectively.
 10. A method of fabricating an integrated circuit structure, the method comprising: forming a fin having a lower fin portion and an upper fin portion; forming a gate stack over the upper fin portion of the fin, the gate stack having a first side opposite a second side; forming a first trench in the fin at the first side of the gate stack and forming a second trench in the fin at the second side of the gate stack; forming a lower semiconductor layer in the first trench and in the second trench, wherein the lower semiconductor layer comprises silicon, germanium and boron, the germanium having an atomic concentration of less than 40%; forming a layer consisting essentially of germanium and boron on the lower semiconductor layer; forming a layer comprising silicon and boron on the layer consisting essentially of germanium and boron; melting and then recrystallizing the layer comprising silicon and boron and the layer consisting essentially of germanium and boron to form a capping semiconductor layer on the lower semiconductor layer.
 11. The method of claim 10, wherein the capping semiconductor layer comprises silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% throughout the capping semiconductor layer.
 12. The method of claim 10, wherein the lower semiconductor layer comprises the germanium having an atomic concentration of less than 30%.
 13. The method of claim 10, wherein the capping semiconductor layer comprises the boron having an atomic concentration of greater than 9E20 cm⁻³.
 14. The method of claim 10, further comprising: forming a metal silicide layer on and in direct contact with the capping semiconductor layer.
 15. The method of claim 14, wherein the metal silicide layer is a silicide of a silicon germanium layer having a composition substantially the same as the composition of the capping semiconductor layer.
 16. A computing device, comprising: a board; and a component coupled to the board, the component including an integrated circuit structure, comprising: a fin having a lower fin portion and an upper fin portion; a gate stack over the upper fin portion of the fin, the gate stack having a first side opposite a second side; a first source or drain structure comprising an epitaxial structure embedded in the fin at the first side of the gate stack, the epitaxial structure comprising a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer; and a second source or drain structure comprising an epitaxial structure embedded in the fin at the second side of the gate stack, the epitaxial structure comprising a lower semiconductor layer and a capping semiconductor layer on the lower semiconductor layer with an abrupt interface between the capping semiconductor layer and the lower semiconductor layer, wherein the lower semiconductor layer of each of the epitaxial structures of the first and second source or drain structures comprises silicon, germanium and boron, the germanium having an atomic concentration of less than 40% at the abrupt interface, and wherein the capping semiconductor layer of each of the epitaxial structures of the first and second source or drain structures comprises silicon, germanium and boron, the germanium having an atomic concentration of greater than 50% at the abrupt interface and throughout the capping semiconductor layer.
 17. The computing device of claim 16, further comprising: a memory coupled to the board.
 18. The computing device of claim 16, further comprising: a communication chip coupled to the board.
 19. The computing device of claim 16, further comprising: a camera coupled to the board.
 20. The computing device of claim 16, further comprising: a battery coupled to the board.
 21. The computing device of claim 16, further comprising: an antenna coupled to the board.
 22. The computing device of claim 16, wherein the component is a packaged integrated circuit die. 